1. Technical Field
The present disclosure is directed to systems and methods for processing an audio signal. In particular, it is directed towards systems and methods for enhancing the real and perceived bass band of an audio signal. Furthermore, it is directed towards systems and methods for enhancing audio performance in mobile audio applications.
2. Background
Audio signal reproduction, particularly in the lower frequency portion of the audio spectrum (e.g. bass spectrum), is generally limited by the nature and design of loudspeakers. In order to provide an audio signal with adequate bass loudness, one generally requires a large speaker area, a large excursion limit, and significant input power in order to move sufficient amounts of the surrounding fluid (e.g. air) to achieve the desired audible loudness.
Under the constraints of limited power availability and severe size restrictions, many modern audio systems employ algorithmic means for enhancing the bass spectrum of an audio signal (e.g. as opposed to utilizing large loudspeakers). It is well known in the art of audio signal processing that the impression of bass in an audio signal may be enhanced by the addition of harmonics of a bass fundamental tone to the audio signal without adding the fundamental tone itself. The harmonic tones suggest a fundamental tone even if the sound lacks a component at the fundamental frequency itself. The brain of a listener generally perceives the pitch of a tone not only by its fundamental frequency, but also via the higher harmonics. Thus, the brain of a listener assumes that the fundamental tone is there when the harmonic tones are registered, and therefore the listener may perceive the same pitch (perhaps with a different timbre) even if the fundamental frequency is missing from a tone. This phenomenon is commonly referred to as the missing fundamental phenomenon or psychoacoustic bass enhancement.
Algorithmic implementation of psychoacoustic bass enhancement may be particularly useful when the audio content is to be reproduced by small loudspeakers as mentioned above (e.g. as is the reality for the majority of modern mobile audio applications).
Yet psychoacoustic bass enhancement itself is not without significant limitations. The process adds a perceived distortion to the audio signal, which may be significant and distracting with certain forms of audio content (e.g. instrumental music).
A purer form of bass signal improvement is a real bass enhancement method, which may provide a superior audio experience versus a psychoacoustic bass enhancement. Yet, real bass enhancement is often hampered by the excursion limits and large signal distortion of the loudspeakers used in an audio processing system.
Thus there is a problem to determine whether or not psychoacoustic bass enhancement and/or real bass enhancement should be implemented in an audio stream and if so, to what degree either or both methods should be implemented.